Do you have an older version, and want to know how the newer versions fit?
Every version we have between v1 and v4 are made on the same "last", which is a plastic mold around which shoes are made. The last shapes the external silhouette and the internal dimensions. So in theory, a size 10 in versions 1, 2, 3, and 4 should all fit the same.
In practice, there is some variation in how they will actually fit.
First, the leather. v1 had a super soft leather, v2 a rather stiff leather, v3 a soft leather, and v4 a softer leather.
Second, v3 and v4 have a thin layer of Poron under the leather footbed, so they have a little less volume than v1 and v2.
Third, newness. A brand-new shoe will fit looser than a worn shoe, because the leather is still taut. As heat, moisture, and movement break in the leather, it will fit closer to your feet.
All that said, if you've ordered from us before, and the size you have fits well, I would recommend ordering the same size in the new version.